Preventing noise from effects in GarageBand

Effects like distortion, overdrive, and amp simulators involve amplification of the Real Instrument's input signal. This amplification may also boost otherwise unnoticeable instrument and background noises. The noise gate can prevent these unwanted, low-level sounds from entering the effects

To reduce noise in a silent passage:

Select the desired track.

Click the headphone icon to solo the track.

Open the Track Info window.

Expand the window so you can see "details".

Click the Gate checkbox.

Start playing the song.

Adjust the Gate slider so that noise disappears from silent passages but the instrument still plays normally elsewhere.